1. Field of the Invention
The present invention relates to an input-output circuit that is disposed between a connector and an internal circuit.
2. Description of the Related Art
Recently, smartphones have been rapidly come into wide use. In many smartphones, in order to improve the designability or decrease the circuit scale, a connector is attempted to be used in common. For example, models only having a micro-USB connector are also available in the market. In such models, in addition to power feeding and data communication, audio signals are transmitted or received through one micro-USB connector. Such connector sharing has been attempted also in other mobile devices such as a cellular phone, a small-sized PC, a digital camera, a portable music player, an IC recorder, and a game machine.
The micro-USB connector is configured by five terminals (pins) including a power supply terminal (VBUS), aground terminal (GND), differential pair terminals (D+ and D−), and an identification line terminal (ID). There are three terminals except for the power supply terminal and the ground terminal and, in order to transmit a video signal and stereo audio signals, it is necessary to use the identification line terminal as well.